Field of the Invention
The present invention relates to a manufacturing method of a diffraction grating.
Description of the Related Art
An Echelle diffraction grating made of a crystal material is a diffraction grating configured to generate diffracted light of a high order, and machining in a ductility mode is required to form grating grooves for a good optical characteristic. A critical cutout thickness exists in the boundary between the ductility mode and a brittle mode. For example, JP 2003-075622 proposes to form the grating grooves in Si or Ge crystal through superfine cutting using a single crystal diamond tool by setting the processed surface to a (111) plane and a cutting direction to the inside of the (111) plane.
However, no prior art propose machining to form the grating grooves in the Echelle diffraction grating made of a CdTe or CdZnTe crystal material, or a stable ductility mode even when a crystal orientation (crystal plane azimuth) and a critical cutout thickness are set to parameters. When the Echelle diffraction grating is used to as a transmission type (immersion type, backside reflection type), it is easily conceivable that its optical performance is affected by both of the long side and the short side. Nevertheless, in common use, the light incident direction is arranged perpendicularly to the short side of the sectional shape of the grating, and thus the quality of the short side is critical as well as the reflective type.